Sprue pins for use in the production of dental and other castings using the lost wax process have been known for some time and are available in various configurations, the most common form consisting of a metal or synthetic resin rod upon which a pattern is mounted. These pins may be mounted directly upon crucible formers and generally permit little facile adjustment of the orientation thereof which is desirable to accommodate the wide variety of casting requirements. It is also quite difficult to utilize two or more of these pins to support and to feed different parts of a relatively large pattern. Furthermore, since these pins are mounted directly and individually to crucible formers, the formers must often have specifically configured mounting portions dependent on the particular application.
Exemplary of another type of synthetic resin sprue pin is that of U.S. Pat. No. 3,340,923 granted to J. W. Benfield on Sept. 12, 1967. Benfield's sprue pin comprises a hollow shaft having an enlarged reservoir portion intermediate its length, the reservoir functioning to provide a cavity for a supply of molten metal during the casting procss which minimizes shrinkage porosity in the casting.
Another type of synthetic resin sprue pin is that of French Letters Patent No. 1,115,559 which comprises a central shaft having a multiplicity of axially and circumferentially spaced branches or runners extending outwardly therefrom. This sprue pin, although it does permit a number of patterns to be mounted thereon, is not adjustable to accommodate patterns of varied configurations.
Accordingly, it is an object of the present invention to provide a novel synthetic resin preform and sprue assembly which is readily and inexpensively manufactured and which permits facile mounting and adjustment of the sprue members thereof to meet the requirements of a wide variety of casting applications.
It is also an object to provide such a preform and sprue assembly wherein the angular orientation of the sprue members is easily adjusted to provide clearance between patterns and to facilitate mounting relatively large patterns upon a plurality of sprue formers.
Another object is to provide such a preform and sprue assembly which permits use of a standard crucible former.
Still another object is to provide a novel and facile method for making investment molds using such a preform and sprue assembly.